1. Field of the Invention
The present invention relates to an image forming apparatus having a multi-electron source and fluorescent substances, and method of manufacturing the image forming apparatus.
2. Description of the Related Art
Flat display apparatuses are thin and lightweight. Attention is therefore being given to them as apparatuses replacing CRT type display apparatuses. A display apparatus using a combination of an electron-emitting device and a fluorescent substance which emits light upon reception of an electron beam, in particular, is expected to have better characteristics than display apparatuses based on other conventional schemes. For example, in comparison with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require a backlight because it is of a self-emission type and that it has a wide view angle.
Conventionally, two types of devices, namely hot and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction emission (SCE) type electron-emitting devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
A known example-of the surface-conduction emission type emitting devices is described in, e.g., M. I. Elinson, xe2x80x9cRadio Eng. Electron Phys., 10, 1290 (1965) and other examples will be described later.
The surface-conduction emission type emitting device utilizes the phenomenon that electrons are emitted from a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction emission type emitting device includes electron-emitting devices using an Au thin film [G. Dittmer, xe2x80x9cThin Solid Filmsxe2x80x9d, 9,317 (1972)], an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)], a carbon thin film [Hisashi Araki et al., xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 15 is a plan view showing the device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction emission type emitting devices. Referring to FIG. 15, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 15. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 15 is set go to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction emission type emitting devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In the forming processing, for example, a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the two ends of the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after the forming processing, electrons are emitted near the fissure.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
FIG. 16 is a sectional view showing the device by C. A. Spindt et al. described above as a typical example of the FE type device structure. Referring to FIG. 16, reference numeral 3010 denotes a substrate; 3011, emitter wiring made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, agate electrode. In this device, a voltage is applied between the emitter cone 3012 and the gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012. As another FE type device structure, there is an example in which an emitter and a gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multi-layered structure of FIG. 16.
A known example of the MIM type electron-emitting devices is described in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961). FIG. 17 shows a typical example of the MIM type device structure. FIG. 17 is a sectional view of the MIM type electron-emitting device. Referring to FIG. 17, reference numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 100 angstrom; and 3023, an upper electrode made of a metal and having a thickness of about 80 to 300 angstrom. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper electrode 3023 and the lower electrode 3021 to emit electrons from the surface of the upper electrode 3023.
Since the above-described cold cathode devices can emit electrons at a temperature lower than that for hot cathode devices, they do not require any heater. The cold cathode device therefore has a structure simpler than that of the hot cathode device and can be micropatterned. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the hot cathode device is low because it operates upon heating by a heater. For this reason, applications of the cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the above surface-conduction emission type emitting devices are advantageous because they have a simple structure and can be easily manufactured. For this reason, many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of surface-conduction emission type emitting devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, a multi-electron source, and the like have been studied.
As an application to image display apparatuses, in particular, as disclosed in the U.S. Pat. No. 5,066,883 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant, image display apparatus using the combination of a surface-conduction emission type emitting device and a fluorescent substance which emits light upon reception of an electron beam has been studied. This type of image display apparatus using the combination of the surface-conduction emission type emitting device and the fluorescent substance is expected to have more excellent characteristics than other conventional image display apparatuses. For example, in comparison with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require a backlight because it is of a self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the present applicant. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat display apparatus reported by R. Meyer et al. [R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)].
An example of an application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the present applicant.
FIG. 18 is a partially cutaway perspective view of an example of a display panel portion as a constituent of a flat image display apparatus, showing the internal structure of the panel.
Referring to FIG. 18, reference numeral 3115 denotes a rear plate; 3116, a side wall; and 3117, a face plate. The rear plate 3115, the side wall 3116, and the face plate 3117 constitute an envelope (airtight container) for maintaining a vacuum in the display panel.
The rear plate 3115 has a substrate 3111 fixed thereon, on which Nxc3x97M cold cathode devices 3112 are formed (M and N are positive integers equal to 2 or more, and properly set in accordance with a desired number of display pixels). The Nxc3x97M cold cathode devices 3112 are arranged in a matrix with M row-direction wirings 3113 and N column-direction wirings 3114. The portion constituted by the substrate 3111, the cold cathode devices 3112, the row-direction wirings 3113, and the column-direction wirings 3114 will be referred to as a multi electron source. An insulating layer (not shown) is formed between each row-direction wiring 3113 and each column-direction wiring 3114, at least at a portion where they cross each other at a right angle, to maintain electric insulation therebetween.
A fluorescent film 3118 made of fluorescent substances is formed on the lower surface of the face plate 3117. The fluorescent film 3118 is coated with red (R), green (G), and blue (B) fluorescent substances (not shown), i.e., three primary color fluorescent substances. Black conductive members (not shown) are provided between the respective color fluorescent substances of the fluorescent film 3118. A metal back 3119 made of aluminum (Al) or the like is formed on the surface of the fluorescent film 3118, located on the rear plate 3115 side. Reference symbols Dx1 to DxM, Dy1 to DyN, and Hv denote electric connection terminals for an airtight structure provided to electrically connect the display panel to an electric circuit (not shown). The terminals Dx1 to DxM are electrically connected to the row-direction wirings 3113 of the multi electron source; the terminals Dy1 to DyN, to the column-direction wirings 3114; and the terminal Hv, to the metal back 3119 of the face plate.
A vacuum of about 10xe2x88x926 Torr is held in the above airtight container. As the display area of the image display apparatus increases, the apparatus requires a means for preventing the rear plate 3115 and the face plate 3117 from being deformed or destroyed by the pressure difference between the inside and outside of the airtight container. A method of thickening the rear plate 3115 and the face plate 3117 will increase the weight of the image display apparatus and cause an image distortion or parallax when the display screen is obliquely seen. In contrast to this, the structure shown in FIG. 18 includes structure support members (called spacers or ribs) 3120 formed of a relatively thin glass plate and used to resist the atmospheric pressure. With this structure, a spacing of sub-millimeters or several millimeters is generally ensured between the substrate 3111 on which the multi electron source is formed and the face plate 3117 on which the fluorescent film 3118 is formed, and a high vacuum is maintained in the airtight container, as described above.
In the image display apparatus using the above display panel, when voltages are applied to the respective cold cathode devices 3112 through the outer terminals Dx1 to DxM and Dy1 to DyN, electrons are emitted by the cold cathode devices 3112. At the same time, a high voltage of several hundred to several kV is applied to the metal back 3119 through the outer terminal Hv to accelerate the emitted electrons to cause them to collide with the inner surface of the face plate 3117. With this operation, the respective color fluorescent substances constituting the fluorescent film 3118 are excited to emit light. As a result, an image is displayed on the screen.
The following problem is posed in the display panel of the image display apparatus described above.
The spacers 3120 arranged in the image display apparatus must be sufficiently positioned and assembled with respect to the substrate 3111 and the face plate 3117. Particularly, the spacers 3120 must be sufficiently positioned with respect to the fluorescent film 3118 on the face plate 3117 side so as not to break display pixels by the spacers; otherwise, the quality of a displayed image may degrade.
If the spacers 3120 are not fixedly arranged in the image display apparatus, the spacers may greatly shift, fall down, and be damaged owing to an external shock to the panel upon or after assembling the airtight container.
The present invention has been made in consideration of the above conventional techniques, and has as its principal object to provide an image forming apparatus having spacers being fixedly fastened inside the apparatus.
It is another object of the present invention to provide an image forming apparatus having spacers which are fixed on an image forming member but only abutted on a member opposing the image forming member, and are fixedly fastened inside the apparatus.
It is still another object of the present invention to provide a method of manufacturing an image forming apparatus, which can facilitate arrangement of spacers in assembling the image forming apparatus.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.